Return error to Angular from Express - angularjs

Question

I have a application where users can add movies to their watchlist. I want to prevent users from adding a movie that already exists in their watchlist.
This my addMovie function in my Angular controller:
$scope.addMovie = function (movie) {
movieFactory.selectMovie(movie).then(function(response){
movieFactory.addMovie(response);
Notification.success(movie.title + ' has been added to your watchlist');
$scope.movies = [];
$scope.overlay = false;
$scope.searchquery = '';
$rootScope.$broadcast('onAddMovieEvent', response);
});
};
I pass the movie object through from my initial ng-click. Then I request a selectMvoie function in the movieFactory that gets the correct movie data from the TMDB api.
Then I call the addMovie function in the movieFactory factory with the response from selectMovie function.
factory.addMovie = function (movie) {
var deferred = $q.defer();
$http({
method: 'POST',
url: '/movies',
data: movie
})
.success(function (data) {
deferred.resolve(data);
})
.catch(function () {
deferred.reject();
});
return deferred.promise;
};
This does a /post request which goes into my Express route:
router.post('/', function(req,res){
pool.getConnection(function(err, connection) {
connection.query('SELECT * FROM user_movieid WHERE movie_id= ? AND userid= ?' ,[req.body.id, req.user.id] , function(err, result) {
for (var i = result.length - 1; i >= 0; i--) {
if (movie.id === result[i].movie_id) {
console.log('exists');
}
}
});
});
})
There's also a connection.query that posts the movie into the database but that's not relevant now.
My situation now is that when I post a movie that already exists my node console shows the message exists but still posts the movie (obviously).
How would I return an "error" status back to my addMovie function in my Angular controller so I can do a if statement to show a different notification?

Answer 1

If you want to keep your API 'restful' then I would return a response with a non 2xx status code. I would think 409 Conflict is appropriate for this case.
router.post('/', function(req,res){
pool.getConnection(function(err, connection) {
connection.query('SELECT * FROM user_movieid WHERE movie_id= ? AND userid= ?' ,[req.body.id, req.user.id] , function(err, result) {
for (var i = result.length - 1; i >= 0; i--) {
if (movie.id === result[i].movie_id) {
console.log('exists');
// choose an appropriate status code, probably a conflict 409 in this case
return res.status(409).send('Movie already exists in your watchlist')
}
}
});
});
})
Then in your Angular code you can notify the user that the movie is already in their list.
$scope.addMovie = function (movie) {
movieFactory.selectMovie(movie).then(function(response){
movieFactory.addMovie(response);
Notification.success(movie.title + ' has been added to your watchlist');
$scope.movies = [];
$scope.overlay = false;
$scope.searchquery = '';
$rootScope.$broadcast('onAddMovieEvent', response);
})
// catch any errors
.catch(function() {
// ideally you should check the status code here and probably handle other non 409 status codes differently
// since this .catch will execute for any other 4xx and 5xx errors
Notification.fail(movie.title + ' is already in your watchlist');
});
};